The mechanisms of action, the regulation and the roles in intermediary metabolism of the enzymes involved in the conversion of thymidine to the pyrimidine nucleotides of RNA in Neurospora crassa are being studied. The enzymes which are being purified and subjected to mechanistic studies include those that catalyze the reactions of the following pathway: (1) pyrimidine deoxyribonucleoside yields ribonucleoside; (2) ribonucleoside yields pyrimidine plus ribose; (3) thymine yields 5-hydroxymethyluracil which (4) yields 5-formyluracil which (5) yields uracil-5-carboxylic acid which (6) yields uracil plus CO2. The studies involving the alpha-ketoglutarate dioxygenase reactions, i.e., 1,3-5, are being emphasized. BIBLIOGRAPHIC REFERENCES: Griswold, W. R., V. O. Madrid, P.M. Shaffer, D.C. Tappen, C.S.G. Pugh and M.T. Abbott. 1976. Regulation of Thymidine Metabolism in Neurospora crassa. J. Bacteriol. (in press). Hsu, C.A., R.A. Jordan and M.T. Abbott, Oxidation of a Carbinol Carbon in the Pyrmidine Deoxyribonucleoside 2'-Hydroxylase Reaction. Fed. Proc. (in press).